The goal of this protocol is to explore changes to microbial communities during the course of hospital care, and to determine the extent to which these alterations affect whether hospitalized patients become colonized with nosocomial bacteria. The study enables collection of clinical specimens and associated medical data to evaluate the natural history and epidemiology of colonization among patients who are expected to be hospitalized for at least seven days. Biological specimens including stool, sputum, and swabs will be collected from CC inpatients at least 2 years of age as frequently as daily through discharge, and at follow-up visits for up to 2 years from the date of enrollment. To understand the dynamics of the fecal and other microbiota of hospitalized patients, this protocol will assess the full complement of the microbial-host-environmental contributions including: (1) microbial genome and community; (2) patients genotype, underlying medical condition, medical treatment; and (3) hospital practices and environment. This protocol has enrolled 26 patients thus far, all meeting high-risk criteria for colonization with multidrug-resistant organisms. The protocol will continue with a focus on epidemiologically significant multidrug-resistant bacteria and yeasts.